Ventilatory and Cardiovascular Responses to Hypoxia and Exercise in Andean Natives Living at Sea Level

Abstract

This study was designed to determine in subjects born at high altitude who move to sea level (HA-SL: born at 3500 m or above; n = 25) whether their cardiorespiratory responses to hypoxia and exercise are similar to those of sea level natives (SL,n = 25). The average age (39 ± 7.3 yr), weight (72 ± 7.3 kg), and height (1.71 ± 0.01 m) did not differ between the SL and HA-SL subjects. All subjects were studied at rest or during exercise (60 W on cycle ergometer) while breathing room air (F_IO2 = 0.21 and P_B = 760) or hypoxia (F_IO2 = 0.115 and PB = 760) in the following order: (1) normoxia at rest (NX-Rs), (2) hypoxia at rest (HX-Rs, 11.5% O₂), hypoxia at exercise (HX-Ex), and normoxia at exercise (NX-Ex). Each period lasted 5 min. In absolute values, HA-SL showed significantly higher ventilation (V_E, L/min) during exercise in both normoxia and hypoxia and higher oxygen saturation (Sa_O2, %) during hypoxia both at rest and in exercise. They also had lower end-tidal CO₂ values (P_ETCO2, torr) at rest in both normoxia and hypoxia, but a higher P_ETCO2 in hypoxic exercise. Heart rate (HR, beats/min) was lower at rest in both normoxia and hypoxia, but higher in exercise. With acute hypoxia, Sa_O2 decreased less in the HA-SL than in the SL at rest (HA-SL, 9.2 ± 0.8; SL, 12.0 ± 0.82) and during exercise (HA-SL, 18.3 ± 1.1; SL, 21.2 ± 1.2). In conclusion, this study shows that HA-SL natives have increased ventilation and heart rate during exercise once their lifelong hypoxia is relieved.